A series of compounds with well defined and characterized responses to membrane potential will be developed. These compounds will bear chromosomes which have been identified by molecular orbital theory calculations as being capable of displaying large linear electrochromic effects. The compounds will be prepared via flexible syntheses which will optimize favorable binding and orientation in membranes. The compounds will then be subjected to a battery of experiments to test their spectroscopic behavior in artificial environments. A transparent multilayer capacitor device with phase locked detection will provide an indication of their response to applied electric fields. A series of experiments with phospholipid vesicles will test their binding, orientation, flipping mobility, and electrochromism in membranes. The probe response will thus be well understood and calibrated. Finally, compounds which give positive results will be screened in a series of natural membranes. A squid axon model will be used to determine the fluorescent lifetimes of the compounds as a function of electric field during a nerve action potential. The dynamic energy linked responses will be determined in a series of sub-cellular membrane preparations using instrumentation designed for sensitive absorbance and emission measurements on these turbid suspensions. Finally, the compounds will be screened for responses with freeze-clamped brain tissue, a live rat brain model, and a heart action potential.